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lTEtI B. ,) OPERATIONAL PLAN Nature and Objectives: This ~roject seeks to extend current knowledge about the artificial and natural nucleation of cirrus(ice crystal)clouds. In addition, we seek to find an efficient way to nroduce widespread cirrus clouds artifiCially. The work covered qy this permit will be the testing of silver iodide as a sublimation nucleus at low temneratures and low sunersaturations with resnect to ice. Any clouds we ~roduce in the atmosphere by this technique will be comnared to natural cirrus clouds and to jet aircraft contrails. Imnlementation: The base of one rations will be Peterson Air Force Base in Colorado Springs. The office location will be 1100 Kachina, Colorado Springs, Colorado B0915 (591-1644). A single-engine propeller-driven modified Schweizer aircraft owned by the Office of Naval Research and onerated by New Mexico Institue of Mining and Technology will be the seeding nlatform. Based on National Weather Service data from circuits A and C as well as FOFAX and on observations of persistent aircraft contrails to the east of Peterson !FB we will try to deCide if a cloudless but ice-supersaturated region exists within the proposed operational area. If things look favorable, the Schweizer will be flown into the operational area at an altitude between 20,000 and 35,000 feet MSL. When its own engine is prOducing a contrail or a small cylinder of carbon dioxide with a trickIer valve on it produces a thin trail of ice crystals from the Wheel struts an attempt will be made to seed a donut-shaped ice cloud with silver iodide. A three-mile diameter circle will be flown . in the region where the engine contrail or carbon dioxide indica~~\a,rt:, supersaturation with respect to ice. One 2B5-gram silver iodide~ill be ignited during the circle. It will be releasing silver iodide at the apnroximate rate of 90 grams per minute and nroducing approximately 1014 nuclei per gram active at the ambient temnerature. (Exact values will vary with altitude and temperature and water vapor mixing ratio.) If an ice crystal cloud is nucleated by the silver iodide, it will be followed as it drifts downstream and disperses. Photographs, ice crystal concentration measurements, temuerature ,measurefuents; 'and; solar",radiation measurements(above.:and below the cloud) will be uerformed. A ground observer will also take photographs and attempt to make radiation measure- ments in the shadow of the donut-shaped cloud. Effects on the Environment: There are no anticipated effects on the environment at the ground. The crystals should sublimate well before they ever fall to the ground. The attenuation of solar radiation will be small because the cloud will be small and moving so that it will not effect any one point at the ground for more' than a few minutes. If the conditions are favorable for our exoeriment, then its effects will be very small comnared to those produced by the normal military and civilian jet aircraft traffic that will be flying in the area.